The invention refers to a fast reactor block with an inner cylindrical vessel for the evacuation of the residual power from the core by natural circulation. It is well-known that in fast reactors of the vessel type it is necessary to separate hydraulically the hot header from the cold header, in order to create a closed circuit for cooling the core.
In currently adopted solutions, the hydraulic separation structure consists of a suitably shaped metal shell, also called the inner vessel, having a complex shape with a certain number of penetrations for housing the pumps and intermediate exchangers. The intermediate exchangers are mostly immersed in the hot header, in which the sodium-sodium exchangers of the auxiliary circuits for evacuating the residual power are also housed.